HARQ feedback for sidelink communication

ABSTRACT

Various aspects of the present disclosure generally relate to wireless communication. In some aspects, a user equipment (UE) may receive one or more sidelink communications on a sidelink between the UE and another UE. The UE may transmit one or more hybrid automatic repeat request (HARQ) feedback communications, associated with the one or more sidelink communications, on the sidelink and in a HARQ feedback resource included in a multi-slot feedback reporting period. The HARQ feedback resource may include a set of negative acknowledgement (NACK) resources or the set of NACK resources and a set of acknowledgement (ACK) resources. Numerous other aspects are provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/842,739, filed on May 3, 2019, entitled “HARQ FEEDBACK FORSIDELINK COMMUNICATION,” which is hereby expressly incorporated byreference herein.

FIELD OF THE DISCLOSURE

Aspects of the present disclosure generally relate to wirelesscommunication and to techniques and apparatuses for hybrid automaticrepeat request (HARQ) feedback for sidelink communication.

BACKGROUND

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power, and/or the like). Examples of such multiple-accesstechnologies include code division multiple access (CDMA) systems, timedivision multiple access (TDMA) systems, frequency-division multipleaccess (FDMA) systems, orthogonal frequency-division multiple access(OFDMA) systems, single-carrier frequency-division multiple access(SC-FDMA) systems, time division synchronous code division multipleaccess (TD-SCDMA) systems, and Long Term Evolution (LTE).LTE/LTE-Advanced is a set of enhancements to the Universal MobileTelecommunications System (UMTS) mobile standard promulgated by theThird Generation Partnership Project (3GPP).

A wireless communication network may include a number of base stations(BSs) that can support communication for a number of user equipment(UEs). A user equipment (UE) may communicate with a base station (BS)via the downlink and uplink. The downlink (or forward link) refers tothe communication link from the BS to the UE, and the uplink (or reverselink) refers to the communication link from the UE to the BS. As will bedescribed in more detail herein, a BS may be referred to as a Node B, agNB, an access point (AP), a radio head, a transmit receive point (TRP),a New Radio (NR) BS, a 5G Node B, and/or the like.

The above multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent user equipment to communicate on a municipal, national,regional, and even global level. New Radio (NR), which may also bereferred to as 5G, is a set of enhancements to the LTE mobile standardpromulgated by the Third Generation Partnership Project (3GPP). NR isdesigned to better support mobile broadband Internet access by improvingspectral efficiency, lowering costs, improving services, making use ofnew spectrum, and better integrating with other open standards usingorthogonal frequency division multiplexing (OFDM) with a cyclic prefix(CP) (CP-OFDM) on the downlink (DL), using CP-OFDM and/or SC-FDM (e.g.,also known as discrete Fourier transform spread OFDM (DFT-s-OFDM)) onthe uplink (UL), as well as supporting beamforming, multiple-inputmultiple-output (MIMO) antenna technology, and carrier aggregation.However, as the demand for mobile broadband access continues toincrease, there exists a need for further improvements in LTE and NRtechnologies. Preferably, these improvements should be applicable toother multiple access technologies and the telecommunication standardsthat employ these technologies.

SUMMARY

In some aspects, a method of wireless communication, performed by a userequipment (UE), may include receiving one or more sidelinkcommunications on a sidelink between the UE and another UE; andtransmitting one or more hybrid automatic repeat request (HARQ) feedbackcommunications, associated with the one or more sidelink communications,on the sidelink and in a HARQ feedback resource included in a multi-slotfeedback reporting period, wherein the HARQ feedback resource includes aset of negative acknowledgement (NACK) resources or the set of NACKresources and a set of acknowledgement (ACK) resources.

In some aspects, a UE for wireless communication may include memory andone or more processors operatively coupled to the memory. The memory andthe one or more processors may be configured to receive one or moresidelink communications on a sidelink between the UE and another UE; andtransmit one or more HARQ feedback communications, associated with theone or more sidelink communications, on the sidelink and in a HARQfeedback resource included in a multi-slot feedback reporting period,wherein the HARQ feedback resource includes a set of NACK resources orthe set of NACK resources and a set of ACK resources.

In some aspects, a non-transitory computer-readable medium may store oneor more instructions for wireless communication. The one or moreinstructions, when executed by one or more processors of a UE, may causethe one or more processors to: receive one or more sidelinkcommunications on a sidelink between the UE and another UE; and transmitone or more HARQ feedback communications, associated with the one ormore sidelink communications, on the sidelink and in a HARQ feedbackresource included in a multi-slot feedback reporting period, wherein theHARQ feedback resource includes: a set of NACK resources, or the set ofNACK resources and a set of ACK resources.

In some aspects, an apparatus for wireless communication may includemeans for receiving one or more sidelink communications on a sidelinkbetween the apparatus and another apparatus; and means for transmittingone or more HARQ feedback communications, associated with the one ormore sidelink communications, on the sidelink and in a HARQ feedbackresource included in a multi-slot feedback reporting period, wherein theHARQ feedback resource includes: a set of NACK resources, or the set ofNACK resources and a set of ACK resources.

Aspects generally include a method, apparatus, system, computer programproduct, non-transitory computer-readable medium, user equipment, basestation, wireless communication device, and processing system assubstantially described herein with reference to and as illustrated bythe accompanying drawings and specification.

The foregoing has outlined rather broadly the features and technicaladvantages of examples according to the disclosure in order that thedetailed description that follows may be better understood. Additionalfeatures and advantages will be described hereinafter. The conceptionand specific examples disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present disclosure. Such equivalent constructions do notdepart from the scope of the appended claims. Characteristics of theconcepts disclosed herein, both their organization and method ofoperation, together with associated advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. Each of the figures is provided for the purposesof illustration and description, and not as a definition of the limitsof the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the above-recited features of the present disclosure can beunderstood in detail, a more particular description, briefly summarizedabove, may be had by reference to aspects, some of which are illustratedin the appended drawings. It is to be noted, however, that the appendeddrawings illustrate only certain typical aspects of this disclosure andare therefore not to be considered limiting of its scope, for thedescription may admit to other equally effective aspects. The samereference numbers in different drawings may identify the same or similarelements.

FIG. 1 is a block diagram conceptually illustrating an example of awireless communication network, in accordance with various aspects ofthe present disclosure.

FIG. 2 is a block diagram conceptually illustrating an example of a basestation in communication with a user equipment (UE) in a wirelesscommunication network, in accordance with various aspects of the presentdisclosure.

FIG. 3A is a block diagram conceptually illustrating an example of aframe structure in a wireless communication network, in accordance withvarious aspects of the present disclosure.

FIG. 3B is a block diagram conceptually illustrating an examplesynchronization communication hierarchy in a wireless communicationnetwork, in accordance with various aspects of the present disclosure.

FIGS. 4A-4C are diagrams illustrating one or more examples of hybridautomatic repeat request (HARQ) feedback for sidelink communication, inaccordance with various aspects of the present disclosure.

FIG. 5 is a diagram illustrating an example process performed, forexample, by a UE, in accordance with various aspects of the presentdisclosure.

DETAILED DESCRIPTION

Various aspects of the disclosure are described more fully hereinafterwith reference to the accompanying drawings. This disclosure may,however, be embodied in many different forms and should not be construedas limited to any specific structure or function presented throughoutthis disclosure. Rather, these aspects are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art. Based on theteachings herein one skilled in the art should appreciate that the scopeof the disclosure is intended to cover any aspect of the disclosuredisclosed herein, whether implemented independently of or combined withany other aspect of the disclosure. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the disclosure set forth herein. Itshould be understood that any aspect of the disclosure disclosed hereinmay be embodied by one or more elements of a claim.

Several aspects of telecommunication systems will now be presented withreference to various apparatuses and techniques. These apparatuses andtechniques will be described in the following detailed description andillustrated in the accompanying drawings by various blocks, modules,components, circuits, steps, processes, algorithms, and/or the like(collectively referred to as “elements”). These elements may beimplemented using hardware, software, or combinations thereof. Whethersuch elements are implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem.

It should be noted that while aspects may be described herein usingterminology commonly associated with 3G and/or 4G wireless technologies,aspects of the present disclosure can be applied in othergeneration-based communication systems, such as 5G and later, includingNR technologies.

FIG. 1 is a diagram illustrating a wireless network 100 in which aspectsof the present disclosure may be practiced. The wireless network 100 maybe an LTE network or some other wireless network, such as a 5G or NRnetwork. The wireless network 100 may include a number of BSs 110 (shownas BS 110 a, BS 110 b, BS 110 c, and BS 110 d) and other networkentities. ABS is an entity that communicates with user equipment (UEs)and may also be referred to as a base station, a NR BS, a Node B, a gNB,a 5G node B (NB), an access point, a transmit receive point (TRP),and/or the like. Each BS may provide communication coverage for aparticular geographic area. In 3GPP, the term “cell” can refer to acoverage area of a BS and/or a BS subsystem serving this coverage area,depending on the context in which the term is used.

A BS may provide communication coverage for a macro cell, a pico cell, afemto cell, and/or another type of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a closed subscriber group (CSG)). ABS for a macro cell may bereferred to as a macro BS. ABS for a pico cell may be referred to as apico BS. A BS for a femto cell may be referred to as a femto BS or ahome BS. In the example shown in FIG. 1, a BS 110 a may be a macro BSfor a macro cell 102 a, a BS 110 b may be a pico BS for a pico cell 102b, and a BS 110 c may be a femto BS for a femto cell 102 c. A BS maysupport one or multiple (e.g., three) cells. The terms “eNB”, “basestation”, “NR BS”, “gNB”, “TRP”, “AP”, “node B”, “5G NB”, and “cell” maybe used interchangeably herein.

In some aspects, a cell may not necessarily be stationary, and thegeographic area of the cell may move according to the location of amobile BS. In some aspects, the BSs may be interconnected to one anotherand/or to one or more other BSs or network nodes (not shown) in thewireless network 100 through various types of backhaul interfaces suchas a direct physical connection, a virtual network, and/or the likeusing any suitable transport network.

Wireless network 100 may also include relay stations. A relay station isan entity that can receive a transmission of data from an upstreamstation (e.g., a BS or a UE) and send a transmission of the data to adownstream station (e.g., a UE or a BS). A relay station may also be aUE that can relay transmissions for other UEs. In the example shown inFIG. 1, a relay station 110 d may communicate with macro BS 110 a and aUE 120 d in order to facilitate communication between BS 110 a and UE120 d. A relay station may also be referred to as a relay BS, a relaybase station, a relay, and/or the like.

Wireless network 100 may be a heterogeneous network that includes BSs ofdifferent types, e.g., macro BSs, pico BSs, femto BSs, relay BSs, and/orthe like. These different types of BSs may have different transmit powerlevels, different coverage areas, and different impacts on interferencein wireless network 100. For example, macro BSs may have a high transmitpower level (e.g., 5 to 40 Watts) whereas pico BSs, femto BSs, and relayBSs may have lower transmit power levels (e.g., 0.1 to 2 Watts).

A network controller 130 may couple to a set of BSs and may providecoordination and control for these BSs. Network controller 130 maycommunicate with the BSs via a backhaul. The BSs may also communicatewith one another, e.g., directly or indirectly via a wireless orwireline backhaul.

UEs 120 (e.g., 120 a, 120 b, 120 c) may be dispersed throughout wirelessnetwork 100, and each UE may be stationary or mobile. A UE maycommunicate with one or more BSs in wireless network 100, maycommunicate directly with another UE (e.g., UE 120 a and UE 120 e, asillustrated in FIG. 1) via a sidelink, and/or the like.

A UE may also be referred to as an access terminal, a terminal, a mobilestation, a subscriber unit, a station, and/or the like. A UE may be acellular phone (e.g., a smart phone), a personal digital assistant(PDA), a wireless modem, a wireless communication device, a handhelddevice, a laptop computer, a cordless phone, a wireless local loop (WLL)station, a tablet, a camera, a gaming device, a netbook, a smartbook, anultrabook, a medical device or equipment, biometric sensors/devices,wearable devices (smart watches, smart clothing, smart glasses, smartwrist bands, smart jewelry (e.g., smart ring, smart bracelet)), anentertainment device (e.g., a music or video device, or a satelliteradio), a vehicular component or sensor, smart meters/sensors,industrial manufacturing equipment, a global positioning system device,or any other suitable device that is configured to communicate via awireless or wired medium.

Some UEs may be considered machine-type communication (MTC) or evolvedor enhanced machine-type communication (eMTC) UEs. MTC and eMTC UEsinclude, for example, robots, drones, remote devices, sensors, meters,monitors, location tags, and/or the like, that may communicate with abase station, another device (e.g., remote device), or some otherentity. A wireless node may provide, for example, connectivity for or toa network (e.g., a wide area network such as Internet or a cellularnetwork) via a wired or wireless communication link. Some UEs may beconsidered Internet-of-Things (IoT) devices, and/or may be implementedas NB-IoT (narrowband internet of things) devices. Some UEs may beconsidered a Customer Premises Equipment (CPE). UE 120 may be includedinside a housing that houses components of UE 120, such as processorcomponents, memory components, and/or the like.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular RAT andmay operate on one or more frequencies. A RAT may also be referred to asa radio technology, an air interface, and/or the like. A frequency mayalso be referred to as a carrier, a frequency channel, and/or the like.Each frequency may support a single RAT in a given geographic area inorder to avoid interference between wireless networks of different RATs.In some cases, NR or 5G RAT networks may be deployed.

In some aspects, two or more UEs 120 (e.g., shown as UE 120 a and UE 120e) may communicate directly using one or more sidelink channels (e.g.,without using a base station 110 as an intermediary to communicate withone another). For example, the UEs 120 may communicate usingpeer-to-peer (P2P) communications, device-to-device (D2D)communications, a vehicle-to-everything (V2X) protocol (e.g., which mayinclude a vehicle-to-vehicle (V2V) protocol, a vehicle-to-infrastructure(V2I) protocol, and/or the like), a mesh network, and/or the like. Inthis case, the UE 120 may perform scheduling operations, resourceselection operations, and/or other operations described elsewhere hereinas being performed by the base station 110.

As indicated above, FIG. 1 is provided as an example. Other examples maydiffer from what is described with regard to FIG. 1.

FIG. 2 shows a block diagram of a design 200 of base station 110 and UE120, which may be one of the base stations and one of the UEs in FIG. 1.Base station 110 may be equipped with T antennas 234 a through 234 t,and UE 120 may be equipped with R antennas 252 a through 252 r, where ingeneral T≥1 and R≥1.

At base station 110, a transmit processor 220 may receive data from adata source 212 for one or more UEs, select one or more modulation andcoding schemes (MCS) for each UE based at least in part on channelquality indicators (CQIs) received from the UE, process (e.g., encodeand modulate) the data for each UE based at least in part on the MCS(s)selected for the UE, and provide data symbols for all UEs. Transmitprocessor 220 may also process system information (e.g., for semi-staticresource partitioning information (SRPI) and/or the like) and controlinformation (e.g., CQI requests, grants, upper layer signaling, and/orthe like) and provide overhead symbols and control symbols. Transmitprocessor 220 may also generate reference symbols for reference signals(e.g., the cell-specific reference signal (CRS)) and synchronizationsignals (e.g., the primary synchronization signal (PSS) and secondarysynchronization signal (SSS)). A transmit (TX) multiple-inputmultiple-output (MIMO) processor 230 may perform spatial processing(e.g., precoding) on the data symbols, the control symbols, the overheadsymbols, and/or the reference symbols, if applicable, and may provide Toutput symbol streams to T modulators (MODs) 232 a through 232 t. Eachmodulator 232 may process a respective output symbol stream (e.g., forOFDM and/or the like) to obtain an output sample stream. Each modulator232 may further process (e.g., convert to analog, amplify, filter, andupconvert) the output sample stream to obtain a downlink signal. Tdownlink signals from modulators 232 a through 232 t may be transmittedvia T antennas 234 a through 234 t, respectively. According to variousaspects described in more detail below, the synchronization signals canbe generated with location encoding to convey additional information.

At UE 120, antennas 252 a through 252 r may receive the downlink signalsfrom base station 110 and/or other base stations and may providereceived signals to demodulators (DEMODs) 254 a through 254 r,respectively. Each demodulator 254 may condition (e.g., filter, amplify,downconvert, and digitize) a received signal to obtain input samples.Each demodulator 254 may further process the input samples (e.g., forOFDM and/or the like) to obtain received symbols. A MIMO detector 256may obtain received symbols from all R demodulators 254 a through 254 r,perform MIMO detection on the received symbols if applicable, andprovide detected symbols. A receive processor 258 may process (e.g.,demodulate and decode) the detected symbols, provide decoded data for UE120 to a data sink 260, and provide decoded control information andsystem information to a controller/processor 280. A channel processormay determine reference signal received power (RSRP), received signalstrength indicator (RSSI), reference signal received quality (RSRQ),channel quality indicator (CQI), and/or the like. In some aspects, oneor more components of UE 120 may be included in a housing.

On the uplink, at UE 120, a transmit processor 264 may receive andprocess data from a data source 262 and control information (e.g., forreports comprising RSRP, RSSI, RSRQ, CQI, and/or the like) fromcontroller/processor 280. Transmit processor 264 may also generatereference symbols for one or more reference signals. The symbols fromtransmit processor 264 may be precoded by a TX MIMO processor 266 ifapplicable, further processed by modulators 254 a through 254 r (e.g.,for DFT-s-OFDM, CP-OFDM, and/or the like), and transmitted to basestation 110. At base station 110, the uplink signals from UE 120 andother UEs may be received by antennas 234, processed by demodulators232, detected by a MIMO detector 236 if applicable, and furtherprocessed by a receive processor 238 to obtain decoded data and controlinformation sent by UE 120. Receive processor 238 may provide thedecoded data to a data sink 239 and the decoded control information tocontroller/processor 240. Base station 110 may include communicationunit 244 and communicate to network controller 130 via communicationunit 244. Network controller 130 may include communication unit 294,controller/processor 290, and memory 292.

Controller/processor 240 of base station 110, controller/processor 280of UE 120, and/or any other component(s) of FIG. 2 may perform one ormore techniques associated with hybrid automatic repeat request (HARQ)feedback for sidelink communication, as described in more detailelsewhere herein. For example, controller/processor 240 of base station110, controller/processor 280 of UE 120, and/or any other component(s)of FIG. 2 may perform or direct operations of, for example, process 500of FIG. 5 and/or other processes as described herein. Memories 242 and282 may store data and program codes for base station 110 and UE 120,respectively. A scheduler 246 may schedule UEs for data transmission onthe downlink and/or uplink.

In some aspects, UE 120 may include means for receiving one or moresidelink communications on a sidelink between the UE and another UE,means for transmitting one or more hybrid automatic repeat request(HARQ) feedback communications, associated with the one or more sidelinkcommunications, on the sidelink and in a HARQ feedback resource includedin a multi-slot feedback reporting period, wherein the HARQ feedbackresource includes a set of negative acknowledgement (NACK) resources orthe set of NACK resources and a set of acknowledgement (ACK) resources,and/or the like. In some aspects, such means may include one or morecomponents of UE 120 described in connection with FIG. 2.

As indicated above, FIG. 2 is provided as an example. Other examples maydiffer from what is described with regard to FIG. 2.

FIG. 3A shows an example frame structure 300 for frequency divisionduplexing (FDD) in a telecommunications system (e.g., NR). Thetransmission timeline for each of the downlink and uplink may bepartitioned into units of radio frames (sometimes referred to asframes). Each radio frame may have a predetermined duration (e.g., 10milliseconds (ms)) and may be partitioned into a set of Z (Z≥1)subframes (e.g., with indices of 0 through Z−1). Each subframe may havea predetermined duration (e.g., 1 ms) and may include a set of slots(e.g., 2^(m) slots per subframe are shown in FIG. 3A, where m is anumerology used for a transmission, such as 0, 1, 2, 3, 4, and/or thelike). Each slot may include a set of L symbol periods. For example,each slot may include fourteen symbol periods (e.g., as shown in FIG.3A), seven symbol periods, or another number of symbol periods. In acase where the subframe includes two slots (e.g., when m=1), thesubframe may include 2L symbol periods, where the 2L symbol periods ineach subframe may be assigned indices of 0 through 2L−1. In someaspects, a scheduling unit for the FDD may be frame-based,subframe-based, slot-based, symbol-based, and/or the like.

While some techniques are described herein in connection with frames,subframes, slots, and/or the like, these techniques may equally apply toother types of wireless communication structures, which may be referredto using terms other than “frame,” “subframe,” “slot,” and/or the likein 5G NR. In some aspects, a wireless communication structure may referto a periodic time-bounded communication unit defined by a wirelesscommunication standard and/or protocol. Additionally, or alternatively,different configurations of wireless communication structures than thoseshown in FIG. 3A may be used.

In certain telecommunications (e.g., NR), a base station may transmitsynchronization signals. For example, a base station may transmit aprimary synchronization signal (PSS), a secondary synchronization signal(SSS), and/or the like, on the downlink for each cell supported by thebase station. The PSS and SSS may be used by UEs for cell search andacquisition. For example, the PSS may be used by UEs to determine symboltiming, and the SSS may be used by UEs to determine a physical cellidentifier, associated with the base station, and frame timing. The basestation may also transmit a physical broadcast channel (PBCH). The PBCHmay carry some system information, such as system information thatsupports initial access by UEs.

In some aspects, a UE (e.g., UE 120 a, UE 120 e, and/or the like) maytransmit, to another UE (e.g., UE 120 a, UE 120 e, and/or the like) andon a sidelink, one or more sidelink communications in a transmissionperiod, which may include one or more slots included in a framestructure 300. In some aspects, the other UE may receive the one or moresidelink communications, may generate feedback for the one or moresidelink communications, may incorporate the feedback into one or morefeedback communications, and may transmit, to the UE and on thesidelink, the one or more feedback communications in one or more symbolsand/or slots included in a reporting period, in a frame structure 300,configured for the sidelink.

In some aspects, the base station may transmit the PSS, the SSS, and/orthe PBCH in accordance with a synchronization communication hierarchy(e.g., a synchronization signal (SS) hierarchy) including multiplesynchronization communications (e.g., SS blocks), as described below inconnection with FIG. 3B.

FIG. 3B is a block diagram conceptually illustrating an example SShierarchy, which is an example of a synchronization communicationhierarchy. As shown in FIG. 3B, the SS hierarchy may include an SS burstset, which may include a plurality of SS bursts (identified as SS burst0 through SS burst B−1, where B is a maximum number of repetitions ofthe SS burst that may be transmitted by the base station). As furthershown, each SS burst may include one or more SS blocks (identified as SSblock 0 through SS block (b_(max_SS-1)), where b_(max_SS-1) is a maximumnumber of SS blocks that can be carried by an SS burst). In someaspects, different SS blocks may be beam-formed differently. An SS burstset may be periodically transmitted by a wireless node, such as every Xmilliseconds, as shown in FIG. 3B. In some aspects, an SS burst set mayhave a fixed or dynamic length, shown as Y milliseconds in FIG. 3B.

The SS burst set shown in FIG. 3B is an example of a synchronizationcommunication set, and other synchronization communication sets may beused in connection with the techniques described herein. Furthermore,the SS block shown in FIG. 3B is an example of a synchronizationcommunication, and other synchronization communications may be used inconnection with the techniques described herein.

In some aspects, an SS block includes resources that carry the PSS, theSSS, the PBCH, and/or other synchronization signals (e.g., a tertiarysynchronization signal (TSS)) and/or synchronization channels. In someaspects, multiple SS blocks are included in an SS burst, and the PSS,the SSS, and/or the PBCH may be the same across each SS block of the SSburst. In some aspects, a single SS block may be included in an SSburst. In some aspects, the SS block may be at least four symbol periodsin length, where each symbol carries one or more of the PSS (e.g.,occupying one symbol), the SSS (e.g., occupying one symbol), and/or thePBCH (e.g., occupying two symbols).

In some aspects, the symbols of an SS block are consecutive, as shown inFIG. 3B. In some aspects, the symbols of an SS block arenon-consecutive. Similarly, in some aspects, one or more SS blocks ofthe SS burst may be transmitted in consecutive radio resources (e.g.,consecutive symbol periods) during one or more slots. Additionally, oralternatively, one or more SS blocks of the SS burst may be transmittedin non-consecutive radio resources.

In some aspects, the SS bursts may have a burst period, whereby the SSblocks of the SS burst are transmitted by the base station according tothe burst period. In other words, the SS blocks may be repeated duringeach SS burst. In some aspects, the SS burst set may have a burst setperiodicity, whereby the SS bursts of the SS burst set are transmittedby the base station according to the fixed burst set periodicity. Inother words, the SS bursts may be repeated during each SS burst set.

The base station may transmit system information, such as systeminformation blocks (SIBs) on a physical downlink shared channel (PDSCH)in certain slots. The base station may transmit control information/dataon a physical downlink control channel (PDCCH) in C symbol periods of aslot, where B may be configurable for each slot. The base station maytransmit traffic data and/or other data on the PDSCH in the remainingsymbol periods of each slot.

As indicated above, FIGS. 3A and 3B are provided as examples. Otherexamples may differ from what is described with regard to FIGS. 3A and3B.

In some cases, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-everything (V2X)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE1) to anothersubordinate entity (e.g., UE2) without relaying that communicationthrough a scheduling entity (e.g., UE or BS), even though the schedulingentity may be utilized for scheduling and/or control purposes. In someexamples, the sidelink signals may be communicated using a licensedspectrum (unlike wireless local area networks, which may use anunlicensed spectrum).

In some cases, a UE may provide, to another UE, feedback associated witha sidelink communication that was received from the other UE on asidelink between the UE and the other UE. The feedback may include, forexample, HARQ feedback (e.g., NACK or ACK for the sidelinkcommunication). The UE may transmit the feedback in one or more HARQfeedback communications. In some cases, a frame structure for thesidelink may include one or more HARQ feedback reporting symbols, ineach slot in the frame structure, that may be used for transmitting theone or more HARQ feedback communications. However, the UE may not needto provide HARQ feedback in every slot in the frame structure, which canresult in unused (and therefore wasted) symbols in each slot, which inturn may reduce the efficiency of the frame structure. Moreover, the oneor more symbols that are configured for transmitting the one or moreHARQ feedback communications may be bound by additional symbols forreception (Rx) to transmission (Tx) turnaround and vice-versa. Since thesidelink may be half-duplex, a UE that is to transmit the one or moreHARQ feedback communications may need one or more additional symbols totransition from Rx mode to Tx mode in order to transmit the one or moreHARQ feedback communications, and then to transition from Tx mode backto Rx mode after the transmission is complete. The addition ofturnaround symbols in each slot in the frame structure can significantlyincrease the overhead of HARQ feedback reporting on the sidelink ifevery slot in the frame structure includes one or more symbols forreporting the HARQ feedback.

Some aspects described herein provide techniques and apparatuses forHARQ feedback for sidelink communication. In some aspects, a UE mayreceive a sidelink communication on a sidelink between the UE and theother UE. The UE may transmit, to the other UE and on the sidelink, oneor more HARQ feedback communications, associated with the sidelinkcommunication, in a HARQ feedback resource during a reporting period.The reporting period may be configured such that the HARQ feedbackresource (e.g., one or more HARQ feedback reporting symbols), fortransmission of the one or more HARQ feedback communications, are onlyincluded in a subset of slots included in the frame structure of thesidelink as opposed to every slot. This may reduce the overhead consumedby HARQ feedback reporting on the sidelink, may reduce the quantity ofunused HARQ feedback reporting symbols, which in turn may increase theefficiency of the frame structure.

The HARQ feedback resource may be partitioned into subsets of resourcesfor different types of HARQ feedback. For example, the HARQ feedbackresource may include a set of NACK resources and a separate set of ACKresources. The set of NACK resources and the set of ACK resources may befurther partitioned into individual NACK resources and ACK resources,respectively. This permits NACK communications to be multiplexed in theset of NACK resources for a plurality sidelink communications (e.g.,associated with the same UE, associated with different UEs, and/or thelike), and permits ACK communications to be multiplexed in the set ofACK resources for a plurality sidelink communications (e.g., associatedwith the same UE, associated with different UEs, and/or the like).

The reporting period and corresponding HARQ feedback resource may be(pre-)configured in all the UEs, and thus may be system wide.Considering the overhead associated with Rx to Tx and Tx to Rxturnaround, system wide resources (i.e., in complete bandwidth) for HARQfeedback may reduce the overhead consumed by Rx to Tx and Tx to Rxturnaround. These HARQ feedback resources appear periodically as per theconfiguration.

During a HARQ feedback resource, other transmitters (e.g., UEs) maycreate a gap in their transmission. To reduce the complexity ofimplementing system-wide feedback, transmission may start only in theboundary of the feedback resources depending on the configuration of theperiod. For example, considering a 2 slot feedback period andconsidering that slots can be aggregated, the transmission can completejust before an upcoming reporting period (e.g., in the case that an evennumber of slots are aggregated) or the transmission can complete oneslot before the upcoming reporting period (in the case that an oddnumber of slots are aggregated).

FIGS. 4A-4C are diagrams illustrating one or more examples 400 of HARQfeedback for sidelink communications, in accordance with various aspectsof the present disclosure. As shown in FIGS. 4A-4C, examples 400 mayinclude a plurality of UEs (e.g., UE 120), such as UE1 and UE2. However,in some aspects, a greater quantity of UEs may be included in examples400. UE1 and UE 2 may be included in a wireless network (e.g., wirelessnetwork 100) and may communicate via a sidelink. In some aspects, thesidelink may be configured with a frame structure, such as a framestructure 300 of FIG. 3A and/or another sidelink frame structure.

As shown in FIG. 4A, the frame structure of the sidelink may include aplurality of transmission periods. In some aspects, a transmissionperiod may include w slots. UE 120 a may transmit, to UE 120 e, one ormore sidelink communications, in the one or more slots included in atransmission period, and/or vice-versa. The quantity of thew slotsincluded in a transmission period may be configurable by a BS includedin the wireless network, by a network function device included in thewireless network, by a network operator of the wireless network, and/orthe like. For example, the quantity of the w slots may be configured forthe entire wireless network (e.g., may be a system-wide transmissionperiod), for a particular UE, for a particular set of UEs, and/or thelike. In some aspects, a transmission period may include a single slot.In some aspects, a transmission period may be a multi-slot transmissionperiod that includes a plurality of slots. In the example illustrated inFIG. 4A, the plurality of transmission periods may each include threeslots.

As further shown in FIG. 4A, the frame structure of the sidelink mayinclude a plurality of multi-slot feedback reporting periods (e.g., afeedback reporting period that is to be used for feedback reporting fora plurality transmission period slots). A feedback reporting period mayinclude x slots (e.g., slot 0 through slot x−1). UE1 and/or UE2 maytransmit, in a feedback reporting period, one or more HARQ feedbackcommunications that include HARQ feedback (e.g., NACK or ACK) for all ora subset of sidelink communications that complete transmission in acorresponding transmission period. In some aspects, HARQ feedbackcommunications that are to be transmitted by a plurality of UEs in aparticular feedback reporting period may be multiplexed together in thefeedback reporting period. For example, the HARQ feedback communicationsmay be time division multiplexed, frequency division multiplexed, and/orthe like.

In some aspects, a transmission period and corresponding feedbackreporting period may be located in adjacent sets of slots in the framestructure. For example, a transmission period may include a first set ofthree contiguous slots and a corresponding feedback reporting period mayinclude a second set of three contiguous slots that commences directlyafter the completion of the first set of three contiguous slots. In someaspects, a transmission period and corresponding feedback reportingperiod may be separated by one or more intervening slots. For example,and as illustrated in FIG. 4A, a transmission period may include a firstset of three contiguous slots, a corresponding feedback reporting periodmay include a second set of three contiguous slots, and the first set ofslots may be separated by two intervening slots.

The one or more HARQ feedback communications that are to be transmittedin a feedback reporting period, may be transmitted in a HARQ feedbackresource included in a single slot or subset of the x slots included inthe feedback reporting period. The HARQ feedback resource may includetime domain resources (e.g., y HARQ feedback reporting symbols (e.g.,one or more contiguous and/or adjacent symbols) and frequency domainresources (e.g., one or more resource blocks (RBs)). In some aspects,they HARQ feedback reporting symbols may include one or more symbols,one or more portions of one or more symbols (e.g., one or more halfsymbols, a 10 μs portion of one or more symbols, and/or the like) thatare located at or near an end of a particular slot included in thefeedback reporting period (e.g., a first slot included in the feedbackreporting period, a last slot included in the feedback reporting period,or another slot included in the feedback reporting period). In someaspects, the y HARQ feedback reporting symbols may include one or moresymbols that are located at or near a beginning of a particular slotincluded in the feedback reporting period. In some aspects, they HARQfeedback reporting symbols may include one or more symbols that arelocated at another location in a slot included in the feedback reportingperiod.

In some aspects, z turnaround symbols may be located adjacent to the yHARQ feedback reporting symbols. For example, one or more turnaroundsymbols may be located before they HARQ feedback reporting symbols andone or more turnaround symbols may be located after they HARQ feedbackreporting symbols. In this way, if a UE that is to transmit the one ormore HARQ feedback communications is receiving sidelink communicationsin the slot that includes they HARQ feedback reporting symbols, the zturnaround symbols provide the UE with a timing buffer to transitionfrom receiving mode to transmission mode in order to transmit the one ormore HARQ communications, and back into receiving mode in order tocontinue receiving the sidelink communications.

The one or more HARQ feedback communications, that are to be transmittedin a feedback reporting period, may be transmitted in a physicalsidelink feedback channel (PSFCH). In some aspects, a UE may transmit aplurality of HARQ feedback communications in the same feedback reportingperiod, a plurality of UEs may transmit respective HARQ feedbackcommunications in the same feedback reporting period, and/or the like.For example, HARQ feedback communications may be multiplexed in thefrequency domain (e.g., using frequency division multiplexing (FDM))and/or in the time domain (e.g., using time division multiplexing (TDM))in the HARQ feedback resource.

In some aspects, different types of HARQ feedback communications may betransmitted in separate associated sets of resources included in theHARQ feedback resource. For example, the sets of resources may include aset of NACK resources (e.g., time and/or frequency resources that are tobe used for transmitting NACK communications) and a separate set of ACKresources (e.g., time and/or frequency resources that are to be used fortransmitting ACK communications). In this case, a UE may transmit one ormore NACK communications using one or more NACK resources included inthe set of NACK resources, and/or may transmit one or more ACKcommunications using one or more ACK resources included in the set ofACK resources. Moreover, a plurality of UEs may transmit NACKcommunications using NACK resources included in the set of NACKresources and/or may transmit ACK communications using ACK resourcesincluded in the set of ACK resources.

In some aspects, the HARQ feedback resource may be configured such thatthe HARQ feedback resources only include a set of NACK resources, andthus only NACK communications are to be transmitted in the HARQ feedbackresource. In this case, one or more UEs may transmit one or more NACKcommunications using NACK resources included in the set of NACKresources.

As shown in FIG. 4B, UE1 and UE2 may perform sidelink communicationsbased at least in part on the frame structure (or similar framestructure) illustrated in FIG. 4A. As shown by reference number 402, UE1may receive, from UE2, one or more sidelink communications in atransmission period on the sidelink. As shown by reference number 404,UE1 may transmit, to UE2, one or more HARQ feedback communications,associated with the one or more sidelink communications, in a multi-slotfeedback reporting period corresponding to the transmission period. Thatis, UE1 may transmit the one or more HARQ feedback communications in theHARQ feedback resource in the feedback reporting period. The one or moreHARQ communications may include one or more NACK communications and/orone or more ACK communications.

In some aspects, UE1 may identify the particular feedback reportingperiod, from a plurality of feedback reporting periods configured forthe sidelink, based at least in part on various factors. In someaspects, UE1 may identify the particular feedback reporting period basedat least in part on a processing capability of UE1. For example, if UE1is capable of receiving the one or more sidelink communications,attempting to decode the one or more sidelink communications, andtransmitting the one or more HARQ feedback communications in the nextoccurring feedback reporting period, UE1 may transmit the one or moreHARQ feedback communications in the next scheduled feedback reportingperiod. Otherwise, UE1 may transmit the one or more HARQ feedbackcommunications in a subsequent feedback reporting period once the one ormore HARQ feedback communications are ready to be transmitted.

In some aspects, UE1 may identify the feedback reporting period based atleast in part on one or more quality of service (QoS) parameters. Forexample, UE1 may identify a feedback reporting period that satisfies alatency parameter for transmitting a HARQ feedback communication. Asanother example, UE1 may identify the feedback reporting period as thenext scheduled feedback reporting period based at least in part on apriority parameter assigned to UE1, may identify the feedback reportingperiod as a subsequent feedback reporting period based at least in parton the priority parameter, assigned to UE1, being a lower priorityrelative to another UE that is to transmit one or more other HARQfeedback communications in the next scheduled feedback reporting period,and/or the like.

Once UE1 has identified the feedback reporting period and HARQ feedbackresource included in the feedback reporting period, UE1 may identify theNACK resources, or NACK resources and ACK resources, included in theHARQ feedback resource that are to be used to transmit the one or moreHARQ feedback communications. In some aspects, UE1 may identify the timeand/or frequency resources based at least in part on a PSFCHconfiguration for the feedback reporting period. The PSFCH configurationmay include a system-wide PSFCH configuration (e.g., a PSFCHconfiguration that is to be used by all UEs in the wireless network),may include a UE-specific PSFCH configuration (e.g., a PFSCHconfiguration that is configured specifically for UE1), a PSFCHconfiguration configured for a set of UEs (e.g., a set of UEscommunicatively connected with a particular base station, a set of UEsassociated with a particular subscriber status, and/or the like), and/orthe like.

In some aspects, if the PSFCH configuration is a PSFCH configurationconfigured for a set of UEs, the quantity of UEs included in the set ofUEs may be based at least in part on whether the HARQ feedback resourceincludes NACK resources only or NACK resources and ACK resources, basedat least in part on a quantity of NACK resources included in the HARQfeedback resource and/or a quantity of ACK resources included in theHARQ feedback resource, and/or the like.

In some aspects, whether the HARQ feedback resource includes NACKresources only or NACK resources and ACK resources may be based at leastin part on the quantity of UEs that are to use the HARQ feedbackresource. For example, if the PSFCH configuration is configured by theUE transmitting the sidelink communications (e.g., UE2), the UEtransmitting the sidelink communications may specify in the PSFCHconfiguration that NACK resources and ACK resources are to be used inthe HARQ feedback resource (e.g., if the quantity of UEs that are to usethe HARQ feedback resource satisfies a threshold quantity) or that onlyNACK resources are to be used in the HARQ feedback resource (e.g., ifthe quantity of UEs that are to use the HARQ feedback resource does notsatisfy the threshold quantity).

In some aspects, UE1 may receive the PSFCH configuration from UE2,another UE included in the wireless network, a base station included inthe wireless network, and/or the like. In some aspects, the PSFCHconfiguration may be included in a downlink control information (DCI)communication, a radio resource control (RRC) communication, a mediumaccess control (MAC) control element (MAC-CE) communication, a sidelinkcontrol information (SCI) communication, and/or the like.

In some aspects, the PSFCH configuration may include an indication ofwhether the HARQ feedback resource includes a set of NACK resources or aset of NACK resources and a set of ACK resources. In some aspects, thePSFCH configuration may include an indication of a quantity of NACKresources included in the set of NACK resources and/or a quantity of ACKresources included in the set of ACK resources, an indication ofrespective identifiers associated with the NACK resources included inthe set of NACK resources (e.g., NACK resource 0, NACK resource 1, andso on) and/or the ACK resources included in the set of ACK resources(e.g., ACK resource 0, ACK resource 1, and so on), and/or the like.

In some aspects, the PSFCH configuration may indicate whether UE1 ispermitted to only transmit NACK communications in the HARQ feedbackresource or permitted to transmit NACK communications and ACKcommunications in the HARQ feedback resource. In some aspects, the HARQfeedback resource may include NACK resources and ACK resources, but UE1may be permitted to use only the NACK resources while other UEs may bepermitted to use the NACK resources and ACK resources. This may occur,for example, based at least in part on a capability of UE1, based atleast in part on the quantity of UEs that are configured to use the HARQfeedback resource, and/or the like.

FIG. 4C illustrates an example configuration of a HARQ feedbackresource. As shown in FIG. 4C, the example HARQ feedback resourceconfiguration may include a set of NACK resources and a separate set ofACK resources. The HARQ feedback resource may be one symbol in the timedomain and one or more RBs in the frequency domain. The set of NACKresources and the set of ACK resources may be TDM in the exampleconfiguration. The set of NACK resources may include a plurality of NACKresources as indicated by identifiers NACK resource 0, NACK resource 1,NACK resource 2, NACK resource 3, and so on. The set of ACK resourcesmay include a plurality of ACK resources as indicated by identifiers ACKresource 0, ACK resource 1, ACK resource 2, ACK resource 3, and so on.

FIG. 4C further illustrates an example mapping of HARQ feedbackcommunications, associated with a plurality of sidelink communications(e.g., sidelink communication 1 through sidelink communication 5), toNACK resources and/or ACK resources included in the HARQ feedbackresource. In some aspects, a UE (e.g., UE1) may determine the mapping ofHARQ feedback communications based at least in part on one or moreformulas and/or one or more parameters. The one or more formulas and/orone or more parameters may be indicated, for example, in a PSFCHconfiguration.

In some aspects, if the UE is to transmit a NACK communication for areceived sidelink communication, the UE may determine the mapping of theNACK communication to a NACK resource based at least in part on NACKresource ID=f (Slot_(Tx), RB_(Tx), UEID_(Tx)), in which the NACKresource identifier for the NACK communication may be determined basedat least in part on a slot identifier associated with a slot in whichthe corresponding sidelink communication was transmitted (e.g., anending slot, a starting slot, and/or the like), an RB identifierassociated with an RB in which the corresponding sidelink communicationwas transmitted (e.g., an ending RB, a starting RB, and/or the like), aUE identifier associated with the UE that transmitted the correspondingsidelink communication (e.g., a layer 1 (L1) identifier, a layer 2 (L2)identifier, and/or the like), and/or the like.

Similarly, if the UE is to transmit an ACK communication for a receivedsidelink communication, the UE may determine the mapping of the ACKcommunication to an ACK resource based at least in part on ACK resourceID=f (Slot_(Tx), RB_(Tx), UEID_(Tx)), in which the ACK resourceidentifier for the ACK communication may be determined based at least inpart on a slot identifier associated with a slot in which thecorresponding sidelink communication was transmitted (e.g., an endingslot, a starting slot, and/or the like), an RB identifier associatedwith an RB in which the corresponding sidelink communication wastransmitted (e.g., an ending RB, a starting RB, and/or the like), a UEidentifier associated with the UE that transmitted the correspondingsidelink communication (e.g., an L1 identifier, an L2 identifier, and/orthe like), and/or the like.

In some aspects, a configuration may be provided such thatdistance-based HARQ feedback resources may be used. In that case, The UEmay also use distance to determine NACK feedback resources along withthe slot identifier, RB identifier, UE identifier, and/or the like. TheUE may determine the NACK feedback resources based at least in part onsteps of configured size distances.

In some aspects, code division multiplexing (CDM) may be used tomultiplex HARQ communications in the HARQ feedback resource. In thiscase, the UE may transmit a HARQ communication with a particular codesequence (e.g., ACK sequence) to uniquely identify the UE relative toother UEs transmitting HARQ communications in the HARQ feedbackresource. In some aspects, CDM may be used with particular types of HARQcommunications and not used with other types of HARQ communications. Forexample, in some cases, CDM may be used with ACK communications but notNACK communications.

In this case, the UE may determine which ACK sequence, to use fortransmitting a particular ACK communication, based at least in part onone or more formulas and/or one or more parameters. The one or moreformulas and/or one or more parameters may be indicated, for example, ina PSFCH configuration. For example, the UE may determine the ACKsequence based at least in part on ACK sequence ID=f(UE_Order_(Rx),Slot_(Tx),RB_(Tx),UEID_(Tx)), in which the ACK sequenceidentifier for the ACK sequence may be determined based at least in parton a slot identifier associated with a slot in which the correspondingsidelink communication was transmitted (e.g., an ending slot, a startingslot, and/or the like), an RB identifier associated with an RB in whichthe corresponding sidelink communication was transmitted (e.g., anending RB, a starting RB, and/or the like), a UE identifier associatedwith the UE that transmitted the corresponding sidelink communication(e.g., L1 identifier, L2 identifier, and/or the like), a UE orderassociated with the UE (e.g., the UE that received the sidelinkcommunication), and/or the like. In some aspects, the UE order mayinclude an index of the order list of all group member L2 identifiers.

In some aspects, the UE order associated with the UE may be anindication of the UE's position within a logical order of UEs inparticular group of UEs. In some aspects, the group of UEs may includethe UEs that are configured to use the HARQ feedback resource. In someaspects, the UE may receive an indication of the UE order associatedwith the UE in a signaling communication, in a PSFCH configuration,and/or the like. The UE order may be determined based at least in parton one or more parameters associated with the UE, such as an L1identifier, an L2 identifier, upper layer signaling information, and/orthe like.

In this way, UE1 may receive a sidelink communication on a sidelinkbetween UE1 and UE2. UE1 may transmit, to UE2 and on the sidelink, oneor more HARQ feedback communications, associated with the sidelinkcommunication, in a HARQ feedback resource during a reporting period.The reporting period may be configured such that the HARQ feedbackresource (e.g., one or more HARQ feedback reporting symbols), fortransmission of the one or more HARQ feedback communications, are onlyincluded in a subset of slots included in the frame structure of thesidelink as opposed to every slot. This may reduce the overhead consumedby HARQ feedback reporting on the sidelink, may reduce the quantity ofunused HARQ feedback reporting symbols, which in turn may increase theefficiency of the frame structure. Moreover, the HARQ feedback resourcemay be partitioned into subsets of resources for transmitting NACKcommunications and/or ACK communications, which permits NACKcommunications and/or ACK communications to be multiplexed in the HARQfeedback resource.

As indicated above, FIGS. 4A-4C are provided as examples. Other examplesmay differ from what is described with respect to FIGS. 4A-4C.

FIG. 5 is a diagram illustrating an example process 500 performed, forexample, by a UE, in accordance with various aspects of the presentdisclosure. Example process 500 is an example where a UE (e.g., UE 120)performs operations associated with HARQ feedback for sidelinkcommunication.

As shown in FIG. 5, in some aspects, process 500 may include receivingone or more sidelink communications on a sidelink between the UE andanother UE (block 510). For example, the UE (e.g., using receiveprocessor 258, transmit processor 264, controller/processor 280, memory282, and/or the like) may receive one or more sidelink communications ona sidelink between the UE and another UE, as described above.

As further shown in FIG. 5, in some aspects, process 500 may includetransmitting one or more HARQ feedback communications, associated withthe one or more sidelink communications, on the sidelink and in a HARQfeedback resource included in a multi-slot feedback reporting period,wherein the HARQ feedback resource includes a set of NACK resources, orand the set of NACK resources and a set of ACK resources (block 520).For example, the UE (e.g., using receive processor 258, transmitprocessor 264, controller/processor 280, memory 282, and/or the like)may transmit one or more HARQ feedback communications, associated withthe one or more sidelink communications, on the sidelink and in a HARQfeedback resource included in a multi-slot feedback reporting period, asdescribed above. In some aspects, the HARQ feedback resource includes aset of NACK resources, or the set of NACK resources and a set of ACKresources.

Process 500 may include additional aspects, such as any single aspect orany combination of aspects described below and/or in connection with oneor more other processes described elsewhere herein.

In a first aspect, the HARQ feedback resource includes the set of NACKresources and the set of ACK resources, and transmitting the one or moreHARQ feedback communications comprises at least one of transmitting aNACK communication, of the one or more HARQ feedback communications, inthe set of NACK resources or transmitting an ACK communication, of theone or more HARQ feedback communications, in the set of ACK resources.In a second aspect, alone or in combination with the first aspect, theHARQ feedback resource includes the set of NACK resources, andtransmitting the one or more HARQ feedback communications comprisestransmitting a NACK communication, of the one or more HARQ feedbackcommunications, in the set of NACK resources.

In a third aspect, alone or in combination with one or more of the firstand second aspects, the HARQ feedback resource includes the set of NACKresources and the set of ACK resources. In a fourth aspect, alone or incombination with one or more of the first through third aspects, theHARQ feedback resource includes the set of NACK resources and the set ofACK resources and the set of NACK resources and the set of ACK resourcesare time division multiplexed in the HARQ feedback resource. In a fifthaspect, alone or in combination with one or more of the first throughfourth aspects, the HARQ feedback resource includes the set of NACKresources and the set of ACK resources, and the set of NACK resourcesand the set of ACK resources are frequency division multiplexed in theHARQ feedback resource.

In a sixth aspect, alone or in combination with one or more of the firstthrough fifth aspects, the HARQ feedback resource includes the set ofNACK resources, process 500 further comprises determining a NACKresource, included in the set of NACK resources, for transmitting theone or more HARQ feedback communications, and transmitting the one ormore HARQ feedback communications comprises transmitting a NACKcommunication, of the one or more HARQ feedback communications, in theNACK resource.

In a seventh aspect, alone or in combination with one or more of thefirst through sixth aspects, determining the NACK resource comprisesdetermining the NACK resource based at least in part on a slot in whicha sidelink communication, of the one or more sidelink communications,associated with the NACK communication was transmitted, an RB in whichthe sidelink communication was transmitted, and an identifier associatedwith the other UE. In an eighth aspect, alone or in combination with oneor more of the first through seventh aspects, the HARQ feedback resourceincludes the set of NACK resources and the set of ACK resources, process500 further comprises determining an ACK resource, included in the setof ACK resources, for transmitting the one or more HARQ feedbackcommunications, and transmitting the one or more HARQ feedbackcommunications comprises transmitting an ACK communication, of the oneor more HARQ feedback communications, in the ACK resource.

In a ninth aspect, alone or in combination with one or more of the firstthrough eighth aspects, determining the ACK resource comprisesdetermining the ACK resource based at least in part on a slot in which asidelink communication, of the one or more sidelink communications,associated with the ACK communication was transmitted, an RB in whichthe sidelink communication was transmitted, and an identifier associatedwith the other UE. In a tenth aspect, alone or in combination with oneor more of the first through ninth aspects, the ACK communicationcomprises an ACK code sequence, and determining the ACK code sequencecomprises determining the ACK code sequence based at least in part on aslot in which the sidelink communication was transmitted, an RB in whichthe sidelink communication was transmitted, an identifier associatedwith the other UE, and a logical order of the UE in a group of UEs.

In an eleventh aspect, alone or in combination with one or more of thefirst through tenth aspects, process 500 further comprises receiving,from the other UE, an indication of whether the HARQ feedback resourceincludes the set of NACK resources or the set of NACK resources and theset of ACK resources, and transmitting the one or more HARQ feedbackcommunications comprises transmitting the one or more HARQ feedbackcommunications based at least in part on the indication. In a twelfthaspect, alone or in combination with one or more of the first througheleventh aspects, the indication is included in a PSFCH configurationfor the multi-slot feedback reporting period, the PSFCH configurationcomprising a system-wide PSFCH configuration, a UE-specific PSFCHconfiguration, or a PSFCH configuration configured for a set of UEs.

In a thirteenth aspect, alone or in combination with one or more of thefirst through twelfth aspects, the PSFCH configuration indicates atleast one of a quantity of NACK resources included in the set of NACKresources or a quantity of ACK resources included in the set of ACKresources. In a fourteenth aspect, alone or in combination with one ormore of the first through thirteenth aspects, the PSFCH configurationcomprises the PSFCH configuration configured for the set of UEs, and aquantity of UEs, included in the set of UEs, is based at least in parton at least one of the quantity of NACK resources included in the set ofNACK resources or the quantity of ACK resources included in the set ofACK resources.

In a fifteenth aspect, alone or in combination with one or more of thefirst through fourteenth aspects, the PSFCH configuration comprises thePSFCH configuration configured for the set of UEs, and a quantity ofUEs, included in the set of UEs, is used to determine whether the HARQfeedback resource includes the set of NACK resources or the set of NACKresources and the set of ACK resources. In a sixteenth aspect, alone orin combination with one or more of the first through fifteenth aspects,receiving the indication comprises receiving the indication from atleast one of the other UE or a base station. In a seventeenth aspect,alone or in combination with one or more of the first through sixteenthaspects, receiving the indication comprises receiving, from the otherUE, the indication in an SCI communication.

In an eighteenth aspect, alone or in combination with one or more of thefirst through seventeenth aspects, the HARQ feedback resource isincluded in a first slot in the multi-slot feedback reporting period. Ina nineteenth aspect, alone or in combination with one or more of thefirst through eighteenth aspects, process 500 includes receive a PSFCHconfiguration indicating at least one of a quantity of NACK resourcesincluded in the set of NACK resources or a quantity of ACK resourcesincluded in the set of ACK resources. In a twentieth aspect, alone or incombination with one or more of the first through nineteenth aspects,process 500 includes determine a NACK resource from the set of NACKresources, or an ACK resource from the set of ACK resources, in which totransmit a HARQ feedback communication of the one or more HARQ feedbackcommunications based at least in part on a slot in which a sidelinkcommunication, of the one or more sidelink communications, associatedwith the HARQ feedback communication was transmitted, and an RB in whichthe sidelink communication was transmitted.

Although FIG. 5 shows example blocks of process 500, in some aspects,process 500 may include additional blocks, fewer blocks, differentblocks, or differently arranged blocks than those depicted in FIG. 5.Additionally, or alternatively, two or more of the blocks of process 500may be performed in parallel.

The foregoing disclosure provides illustration and description, but isnot intended to be exhaustive or to limit the aspects to the preciseform disclosed. Modifications and variations may be made in light of theabove disclosure or may be acquired from practice of the aspects.

As used herein, the term “component” is intended to be broadly construedas hardware, firmware, and/or a combination of hardware and software. Asused herein, a processor is implemented in hardware, firmware, and/or acombination of hardware and software.

As used herein, satisfying a threshold may, depending on the context,refer to a value being greater than the threshold, greater than or equalto the threshold, less than the threshold, less than or equal to thethreshold, equal to the threshold, not equal to the threshold, and/orthe like.

It will be apparent that systems and/or methods described herein may beimplemented in different forms of hardware, firmware, and/or acombination of hardware and software. The actual specialized controlhardware or software code used to implement these systems and/or methodsis not limiting of the aspects. Thus, the operation and behavior of thesystems and/or methods were described herein without reference tospecific software code—it being understood that software and hardwarecan be designed to implement the systems and/or methods based, at leastin part, on the description herein.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure of various aspects. In fact, many ofthese features may be combined in ways not specifically recited in theclaims and/or disclosed in the specification. Although each dependentclaim listed below may directly depend on only one claim, the disclosureof various aspects includes each dependent claim in combination withevery other claim in the claim set. A phrase referring to “at least oneof” a list of items refers to any combination of those items, includingsingle members. As an example, “at least one of: a, b, or c” is intendedto cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combinationwith multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c,a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering ofa, b, and c).

No element, act, or instruction used herein should be construed ascritical or essential unless explicitly described as such. Also, as usedherein, the articles “a” and “an” are intended to include one or moreitems, and may be used interchangeably with “one or more.” Furthermore,as used herein, the terms “set” and “group” are intended to include oneor more items (e.g., related items, unrelated items, a combination ofrelated and unrelated items, and/or the like), and may be usedinterchangeably with “one or more.” Where only one item is intended, thephrase “only one” or similar language is used. Also, as used herein, theterms “has,” “have,” “having,” and/or the like are intended to beopen-ended terms. Further, the phrase “based on” is intended to mean“based, at least in part, on” unless explicitly stated otherwise.

What is claimed is:
 1. A method of wireless communication performed by auser equipment (UE), comprising: receiving a physical sidelink feedbackchannel (PSFCH) configuration indicating at least one of: a quantity ofnegative acknowledgement (NACK) resources included in a set of NACKresources, or a quantity of acknowledgement (ACK) resources included ina set of ACK resources; receiving a plurality of sidelink communicationsin one or more transmission period slots in a frame structure of asidelink between the UE and another UE; and transmitting a plurality ofhybrid automatic repeat request (HARQ) feedback communications,associated with the plurality of sidelink communications, on thesidelink and in a HARQ feedback resource included in a multi-slotfeedback reporting period of the sidelink, wherein the multi-slotfeedback reporting period is a subset of slots included in the framestructure of the sidelink, wherein the subset of slots are differentfrom the one or more transmission period slots, wherein the HARQfeedback resource includes one or more symbols in the subset of slots orone or more portions of the one or more symbols, and wherein the HARQfeedback resource includes: the set of (NACK)NACK resources, or the setof NACK resources and the set of ACK resources.
 2. The method of claim1, wherein the HARQ feedback resource includes: the set of NACKresources and the set of ACK resources; and wherein transmitting theplurality of HARQ feedback communications comprises at least one of:transmitting a NACK communication, of the plurality of HARQ feedbackcommunications, in the set of NACK resources, or transmitting an ACKcommunication, of the plurality of HARQ feedback communications, in theset of ACK resources.
 3. The method of claim 1, wherein the HARQfeedback resource includes: the set of NACK resources; and whereintransmitting the plurality of HARQ feedback communications comprises:transmitting a NACK communication, of the plurality of HARQ feedbackcommunications, in the set of NACK resources.
 4. The method of claim 1,wherein the HARQ feedback resource includes: the set of NACK resourcesand the set of ACK resources.
 5. The method of claim 1, wherein the HARQfeedback resource includes: the set of NACK resources and the set of ACKresources; and wherein the set of NACK resources and the set of ACKresources are time division multiplexed in the HARQ feedback resource.6. The method of claim 1, wherein the HARQ feedback resource includes:the set of NACK resources and the set of ACK resources; and wherein theset of NACK resources and the set of ACK resources are frequencydivision multiplexed in the HARQ feedback resource.
 7. The method ofclaim 1, wherein the HARQ feedback resource includes: the set of NACKresources; wherein the method further comprises: determining a NACKresource, included in the set of NACK resources, for transmitting a HARQfeedback communication of the plurality of HARQ feedback communications;and wherein transmitting the plurality of HARQ feedback communicationscomprises: transmitting a NACK communication, of the plurality of HARQfeedback communications, in the NACK resource.
 8. The method of claim 7,wherein determining the NACK resource comprises: determining the NACKresource based at least in part on: a slot in which a sidelinkcommunication, of the plurality of sidelink communications, associatedwith the NACK communication was transmitted, a resource block (RB) inwhich the sidelink communication was transmitted, and an identifierassociated with the other UE.
 9. The method of claim 1, wherein the HARQfeedback resource includes: the set of NACK resources and the set of ACKresources; wherein the method further comprises: determining an ACKresource, included in the set of ACK resources, for transmitting a HARQfeedback communication of the plurality of HARQ feedback communications;and wherein transmitting the plurality of HARQ feedback communicationscomprises: transmitting an ACK communication, of the plurality of HARQfeedback communications, in the ACK resource.
 10. The method of claim 9,wherein determining the ACK resource comprises: determining the ACKresource based at least in part on: a slot in which a sidelinkcommunication, of the plurality of sidelink communications, associatedwith the ACK communication was transmitted, a resource block (RB) inwhich the sidelink communication was transmitted, and an identifierassociated with the other UE.
 11. The method of claim 9, wherein the ACKcommunication comprises: an ACK code sequence; and wherein determiningthe ACK code sequence comprises: determining the ACK code sequence basedat least in part on: a slot in which a sidelink communication wastransmitted, a resource block (RB) in which the sidelink communicationwas transmitted, an identifier associated with the other UE, and alogical order of the UE in a group of UEs.
 12. The method of claim 1,further comprising: receiving, from the other UE, an indication ofwhether the HARQ feedback resource includes the set of NACK resources orthe set of NACK resources and the set of ACK resources; and whereintransmitting the plurality of HARQ feedback communications comprises:transmitting the plurality of HARQ feedback communications based atleast in part on the indication.
 13. The method of claim 12, wherein theindication is included in a the PSFCH configuration; and wherein thePSFCH configuration comprises: a system-wide PSFCH configuration, aUE-specific PSFCH configuration, or a PSFCH configuration configured fora set of UEs.
 14. The method of claim 13, wherein the PSFCHconfiguration comprises: the PSFCH configuration configured for the setof UEs; and wherein a quantity of UEs, included in the set of UEs, isbased at least in part on at least one of: the quantity of NACKresources included in the set of NACK resources, or the quantity of ACKresources included in the set of ACK resources.
 15. The method of claim13, wherein the PSFCH configuration comprises: the PSFCH configurationconfigured for the set of UEs; and wherein a quantity of UEs, includedin the set of UEs, is used to determine whether the HARQ feedbackresource includes the set of NACK resources or the set of NACK resourcesand the set of ACK resources.
 16. The method of claim 12, whereinreceiving the indication comprises: receiving the indication from atleast one of: the other UE, or a base station (BS).
 17. The method ofclaim 12, wherein receiving the indication comprises: receiving, fromthe other UE, the indication in a sidelink control information (SCI)communication.
 18. The method of claim 1, wherein the HARQ feedbackresource is included in a first slot in the multi-slot feedbackreporting period.
 19. A user equipment (UE) for wireless communication,comprising: a memory; and one or more processors operatively coupled tothe memory, the memory and the one or more processors configured to:receive a physical sidelink feedback channel (PSFCH) configurationindicating at least one of: a quantity of negative acknowledgement(NACK) resources included in a set of NACK resources, or a quantity ofacknowledgement (ACK) resources included in a set of ACK resources;receive a plurality of sidelink communications in one or moretransmission period slots in a frame structure of a sidelink between theUE and another UE; and transmitting a plurality of hybrid automaticrepeat request (HARQ) feedback communications, associated with theplurality of sidelink communications, on the sidelink and in a HARQfeedback resource included in a multi-slot feedback reporting period ofthe sidelink, wherein the multi-slot feedback reporting period is asubset of slots included in the frame structure of the sidelink, whereinthe subset of slots are different from the one or more transmissionperiod slots, wherein the HARQ feedback resource includes one or moresymbols in the subset of slots or one or more portions of the one ormore symbols, and wherein the HARQ feedback resource includes: the setof (NACK)NACK resources, or the set of NACK resources and the set of ACKresources.
 20. The UE of claim 19, wherein the HARQ feedback resource isincluded in a first slot in the multi-slot feedback reporting period.21. The UE of claim 19, wherein the one or more processors are furtherconfigured to: determine a NACK resource from the set of NACK resources,or an ACK resource from the set of ACK resources, in which to transmit aHARQ feedback communication of the plurality of HARQ feedbackcommunications based at least in part on: a slot in which a sidelinkcommunication, of the plurality of sidelink communications, associatedwith the HARQ feedback communication was transmitted, and a resourceblock (RB) in which the sidelink communication was transmitted.
 22. Anon-transitory computer-readable medium storing one or more instructionsfor wireless communication, the one or more instructions comprising: oneor more instructions that, when executed by one or more processors of auser equipment (UE), cause the one or more processors to: receive aphysical sidelink feedback channel (PSFCH) configuration indicating atleast one of: a quantity of negative acknowledgement (NACK) resourcesincluded in a set of NACK resources, or a quantity of acknowledgement(ACK) resources included in a set of ACK resources; receive a pluralityof sidelink communications in one or more transmission period slots in aframe structure of a sidelink between the UE and another UE; andtransmit a plurality of hybrid automatic repeat request (HARQ) feedbackcommunications, associated with the plurality of sidelinkcommunications, on the sidelink and in a HARQ feedback resource includedin a multi-slot feedback reporting period, wherein the multi-slotfeedback reporting period is a subset of slots included in the framestructure of the sidelink, wherein the subset of slots are differentfrom the one or more transmission period slots, wherein the HARQfeedback resource includes one or more symbols in the subset of slots orone or more portions of the one or more symbols, and wherein the HARQfeedback resource includes: the set of (NACK)NACK resources, or the setof NACK resources and the set of ACK resources.
 23. The non-transitorycomputer-readable medium of claim 22, wherein the HARQ feedback resourceis included in a first slot in the multi-slot feedback reporting period.24. The non-transitory computer-readable medium of claim 22, wherein theone or more instructions, when executed by the one or more processors,further cause the one or more processors to: determine a NACK resourcefrom the set of NACK resources, or an ACK resource from the set of ACKresources, in which to transmit a HARQ feedback communication of theplurality of HARQ feedback communications based at least in part on: aslot in which a sidelink communication, of the plurality of sidelinkcommunications, associated with the HARQ feedback communication wastransmitted, and a resource block (RB) in which the sidelinkcommunication was transmitted.
 25. An apparatus for wirelesscommunication, comprising: means for receiving a physical sidelinkfeedback channel (PSFCH) configuration indicating at least one of: aquantity of negative acknowledgement (NACK) resources included in a setof NACK resources, or a quantity of acknowledgement (ACK) resourcesincluded in a set of ACK resources; means for receiving a plurality ofsidelink communications in one or more transmission period slots in aframe structure of a sidelink between the apparatus and anotherapparatus; and means for transmitting a plurality of hybrid automaticrepeat request (HARQ) feedback communications, associated with theplurality of sidelink communications, on the sidelink and in a HARQfeedback resource included in a multi-slot feedback reporting period ofthe sidelink, wherein the multi-slot feedback reporting period is asubset of slots included in the frame structure of the sidelink, whereinthe subset of slots are different from the one or more transmissionperiod slots, wherein the HARQ feedback resource includes one or moresymbols in the subset of slots or one or more portions of the one ormore symbols, and wherein the HARQ feedback resource includes: the setof (NACK)NACK resources, or the set of NACK resources and the set of ACKresources.
 26. The apparatus of claim 25, wherein the HARQ feedbackresource is included in a first slot in the multi-slot feedbackreporting period.
 27. The UE of claim 19, wherein the HARQ feedbackresource includes: the set of NACK resources; wherein the one or moreprocessors are further configured to: determine a NACK resource,included in the set of NACK resources, for transmitting a HARQ feedbackcommunication of the plurality of HARQ feedback communications; andwherein the one or more processors, when transmitting the plurality ofHARQ feedback communications, are configured to: transmit a NACKcommunication, of the plurality of HARQ feedback communications, in theNACK resource.
 28. The UE of claim 27, wherein the one or moreprocessors, when determining the NACK resource, are configured to:determine the NACK resource based at least in part on: a slot in which asidelink communication, of the plurality of sidelink communications,associated with the NACK communication was transmitted, a resource block(RB) in which the sidelink communication was transmitted, and anidentifier associated with the other UE.
 29. The UE of claim 19, whereinthe HARQ feedback resource includes: the set of NACK resources and theset of ACK resources; wherein the one or more processors are furtherconfigured to: determine an ACK resource, included in the set of ACKresources, for transmitting a HARQ feedback communication of theplurality of HARQ feedback communications; and wherein the one or moreprocessors, when transmitting the plurality of HARQ feedbackcommunications, are configured to: transmit an ACK communication, of theplurality of HARQ feedback communications, in the ACK resource.
 30. TheUE of claim 29, wherein the one or more processors, when determining theACK resource, are configured to: determine the ACK resource based atleast in part on: a slot in which a sidelink communication, of theplurality of sidelink communications, associated with the ACKcommunication was transmitted, a resource block (RB) in which thesidelink communication was transmitted, and an identifier associatedwith the other UE.